First of all, a bit more info would be useful.
- Do you export to a server?
- With which browser are you viewing the page?
- Does it work in the preview?
- Which font are you trying to export?
Also, a .capx is always helpful.
Without the .capx, I can't assume really much.
It might be the case that the font is not web-safe, but to tell, I'll have to know more about your project.